GS-34 PA for 23cmWatercooled version, designed and built byRW1AWClick on callsign for e-mail

This page details the GS-34 design shown on the previous page, repackaged in a water-cooled version. He uses it
at home at the 200W output level. He tested it at home in St. Petersburg, and in Estonia at
the XXXIX VHF/UHF/SHF festival, 28-29 June 2002. The picture below shows the PA after the
demonstration at the festival. It does 400W out for low duty cycle transmissions like SSB,
with minimal thermal drift!

The GS-34 PA as it appears in the RW1AW
shack. Driven by the barefoot TS-2000X (Note the TS-2000X is reading 1296.05000 MHz), with
a little over 13dB gain, it provides 200W drift-free output. With 18 to 22W drive, one could
achieve 400W output, or more, at 48 to 50% efficiency. At low duty cycles (such as SSB),
there is little thermal drift!

All three modules, with top of cabinets
removed. From left to right, the cooling resevoir, the PA and the power supply. All
connections are in place between the modules.

The coolant module, with the 2.5
liter reservoir and showing the rear panel. This module includes an automatic mechanism for
PA shutdown if water flow stops for any reason. The pump is also in this enclosure. The
tank, pump and water tubing for this module are shown at right.

The PA with views of both front and
rear panels. It is the same as the original design except water cooled. The vacuum
relay removes B+ if water flow stops.

Another look at the originalGS-34 PA design. As noted above, this amplifier
can do approximately 400W to 450W output at very low duty cycles without significant
drift caused by thermal problems.
The cooling module is capable of cooling two such PAs, and
if two were paralleled using proper combiners, 800W of low duty cycle RF from 40W drive should
be attainable.

The completed water cooled PA is shown
at right. Click HERE
for construction details of PA cavity.